SP1.7 modification request (xover frequency range)

jradley · « **on:** 15 Apr 2004, 11:47 am »

Hi,

I have an enhancement request/suggestion for the SP1.7.

My system comprises an SP1.7/6BSST with PMC IB1's for fronts and a CB6 for centre. I don't have a sub.

Naturally I set the front speakers to "Large" in the set-up, but the centre is more of an issue. The CB6 is good for 35Hz and I would like to direct any bass down to that frequency to it. Anything lower should go to the IB1's, which are better capable of dealing with it.

If I set the centre channel to "small" then the lowest xover frequency I can have is 60Hz - I'm not sure if this is an arbitary value or one set by THX. Either way, using this loses almost an octave of sound that this speaker could handle. If I set it to "Large" then it will get the full whack of bass below 35Hz which really should be going to the fronts.

Would it be at all possible to extend the xover frequency range to include say 40Hz ?

Let me know your thoughts.

Cheers,

John
(p.s. I know - I should have bought an IB1MC for the centre instead of the CB6 but it would never have fitted under my telly

)

nicolasb · « **Reply #1 on:** 15 Apr 2004, 02:35 pm »

The latest version of the SP1.7 software allows cross-overs down to 25Hz. You could ask Bryston tech support to send you a new EPROM.

However (as you probably know) you should never set the cross-over below 80Hz if you're listening to a 5.1 or 6.1 movie soundtrack. (Any value is fine for stereo).

jradley · « **Reply #2 on:** 15 Apr 2004, 02:43 pm »

Hi,

Thanks for the reply. That is really great news.

The odd thing is, my SP1.7 is brand new - in so much as I ordered it late February and received it just 2 weeks ago. The date code on it however is October of last year.

PMC are replacing the unit anyway as the remote has a dent in it and the front panel had a scratch in it too. Hopefully the replacement will be a newer build and will come with the new firmware version.

BTW, why shouldn't the xover frequency be set to below 80Hz - I really don't know ?

Thanks again,

John

jethro · « **Reply #3 on:** 15 Apr 2004, 09:35 pm »

John,

The remote must have taken a really good hit to cause a dent !

There is a thread from a while back that discusses cross-over frequencies. A search will probably find it if you haven't already done so. This old thread assumes a sub-woofer is being used, so your case is different.

I was wondering if the .1 channel in your setup gets routed to the fronts since they are set to large or if the .1 is thrown away. I always use a sub for 5.1 so I've never tried it and I don't have a good test DVD for testing this out.

When the sub-woofer is present, the sub-crossover is also applied to the .1 channel. Therefore, if some of your speakers are set to small, and the sub crossover is set too low (< 80 Hz), then the .1 channel is also low-passed and information may be lost in the .1 channel. I currently have all of my speakers set to large and the sub crossover set to 120 Hz. I have IB1 fronts which can handle the large setting, but my center (B&W LCR6S2) and rears (B&W 601S2s) aren't really made for the large setting, but I set them large anyways. I haven't decided yet if this is the best setup or not.
I hope to go to IB1's (or better) all around eventuallly.

So to sum up, Nicolas may be referring to the "bug" that most processors have with regards to handling the .1 channel.

jethro · « **Reply #4 on:** 15 Apr 2004, 10:04 pm »

John,

I also meant to ask whether you had a chance to compare the IB1MC and the CB6 ?

Thanks.

jradley · « **Reply #5 on:** 16 Apr 2004, 10:40 am »

Hi Jethro,

Thanks for the hint to search previous threads for cross over info - interesting stuff.

I'm pretty sure that when no sub is configured, the .1 info is sent to the fronts if set to large. At least, the rattling windows would suggest that is the case

I could be wrong though. I'm not sure if the .1 is also sent to the centre if set to large as well (anyone know ?)

It's an interesting comment about the cross over also being applied to the sub and on one hand makes sense, but also doesn't. It's an easy decision to route any bass information for any speaker that can't handle it (ie small) to the sub but not such an easy decision as to where to route higher frequency bass in the .1 channel when the sub can't hajndle it. It would make sense to send this to the fronts.

I may end up getting a sub at some stage but right now funds declare it has to wait. The problem is getting a sub which can deliver bass as cleanly as the IB1's (up to the point where they run out of steam).

I haven't yet done a good test on the CB6 - my initial impression though is that it sounds a little "boxy". However, this is based on about 10 miuntes of listening, it's not properly positioned, not run-in or calibrated for volume or delay and so I'd take this with a pinch of salt.

Cheers,

John

nicolasb · « **Reply #6 on:** 16 Apr 2004, 11:34 am »

Quote

So to sum up, Nicolas may be referring to the "bug" that most processors have with regards to handling the .1 channel.

Nicolas is indeed referring to that, yes.

The way the subwoofer output is calculated, if you have any speakers set to Small, is to mix the actual LFE signal with the all of the "Small" channels, then apply a low-pass filter, and send what's left to the sub. So if you have the cross-over set to (say) 40Hz, then anything above 40Hz in the LFE channel (the .1 of 5.1) is lost. (N.B. it is NOT sent to one of the other speakers, it is simply thrown away).

This isn't a problem with stereo sources, because then there's no LFE channel to begin with.

I would speculate that you would get the same problem if you're not using a subwoofer - the only difference there is that the Sub signal is redirected to the front (Large) speakers.